In the dense forests of Costa Rica’s Osa Peninsula, roads cut through continuous tree cover and create hazards for animals that rarely descend to the ground. Conservation groups have responded by installing canopy bridges, simple structures that link trees on either side of the pavement. A new analysis of camera-trap footage collected across three years now provides clearer evidence of how these crossings perform over time.
Roads Fragment Habitats for Arboreal Species
Many mammals and primates spend their lives in the upper layers of the forest and cross open ground only when necessary. When a road interrupts that canopy, the animals face direct exposure to vehicles and predators. The Osa Peninsula holds high biodiversity, yet its road network continues to expand, making safe passage a growing concern for local wildlife managers.
Earlier efforts to install canopy bridges relied on short monitoring periods, often a single year or less. Without extended records, it remained difficult to judge whether animals gradually accepted the structures or whether certain designs performed better than others. The recent project addressed that gap by examining footage from 17 bridges installed by the nonprofit Osa Conservation.
Three Years of Camera Data Show Steady Increase in Use
Researchers reviewed thousands of video clips recorded between late 2020 and mid-2023. The total count reached 2,231 confirmed crossings by arboreal mammals. Use of the bridges rose consistently across the study period, suggesting that animals became more familiar with the routes as time passed.
Lead author Marion Fischer, a doctoral student at the University of French Guiana, collaborated with Osa Conservation to examine the full dataset. The extended timeframe allowed the team to observe patterns that shorter studies had missed. Bridges of different lengths and materials showed varying levels of activity, pointing to design features that may encourage greater adoption.
Still, the findings carry limits. The cameras captured only animals that approached the structures; they could not record every possible crossing or confirm whether ground-level movements declined. Researchers note that continued observation will help determine whether the upward trend holds in future years.
Species That Cross and Species That Do Not
At least 13 species of tree-dwelling mammals appeared on the footage. Among them were the common opossum and the Mexican hairy dwarf porcupine, both known to suffer vehicle collisions when they attempt to cross roads at ground level. White-faced capuchin monkeys and squirrel monkeys also used the bridges regularly.
Larger primates such as howler monkeys and spider monkeys were absent from the records. Their absence may reflect differences in movement patterns, body size, or comfort with the bridge materials. The study does not yet explain why these species avoided the structures, leaving an open question for follow-up work.
What Remains Unknown and What Comes Next
The data indicate that canopy bridges can serve as functional links for some vulnerable species, yet questions persist about long-term population effects. It is still unclear whether the crossings reduce overall road mortality or simply shift some animals to safer routes. Additional monitoring at more sites and across different forest types would strengthen the evidence base.
Conservation planners continue to weigh bridge design, placement, and maintenance costs against other mitigation options. The Costa Rican results offer practical guidance while underscoring the value of sustained observation rather than one-time assessments. As road networks grow in tropical regions, such information helps prioritize investments that genuinely support forest connectivity.
